Using the birth year from the 1911 census, this is the only Muriel Robinson birth in the area of St Martin in the Fields around 1880:

Name:                   Mother's Maiden Surname:
ROBINSON, MURIEL        WINN  
GRO Reference: 1879  S Quarter in STRAND  Volume 01B  Page 674
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Remarkably there was also this baptism and ancestry provided the image of the Register page:

“                        Page 384
“BAPTISMS solemnized in the Parish of ST MARTIN IN THE FIELDS in the
“  County of MIDDLESEX in the Year 1879
“. . . .
“Born:                June 12th 1879
“When baptized:       August 31st
“No:                  203
“Child’s forename:    Muriel Alice
“Parents’ forenames:  Joseph Alexander & Emily
“Parents’ surname:    Robinson
“Abode:               22 Whitcomb St
“Profession:          Licenced Victualler
“Celebrant:           Philip Hale, Off. Min.

Note that this is the first information of her father’s name.
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This very much looks like the young lady in 1911 who confidently made the Marriage Licence Allegation in 1914 and was in 1911 living at 175 Clapham Road, Lambeth, London SW:

First name(s)  Last name  Relationship  Marital status  Sex  Age  Birth year  Occupation  Birth place

Emily           Robinson  Head  W  F  53  1858  None                              Shoreditch, Mx
Muriel Alice    Robinson  Daur  S  F  31  1880  Instructress of domestic science  St Martins in Fields
Louisa Sebylla  Heinrich  None  S  F  40  1871  Solictor's clerk                  Leyton Essex
Ruby Wilhelmin  Heinrich  None  S  F  32  1879  Solicitor's clerk                 Leyton Essex
Emma Lois       Collyns   None  S  F  20  1891  Instructress of domestic science  Stoke Plymouth
Helen           Harris    None  S  F  35  1876  Instructress of domestic science  Hartlebury, Worcs

1911 ref: RG14PN2026 RG78PN71 RD25 SD3 ED20 SN351

On the source form her mother reported she had had two children both of whom were still alive.
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Following on from all the above, this looks very much like a three generation family of her, her daughter and her mother all living at Cambridge Street, Pimlico, City Of Westminster, City of Westminster, London, the only problem being her own birth date:

First name(s)  Last name(s)  Birth date  Sex  Occupation  Marital status  Schedule  Schedule sub number
Muriel A    Drake     08 Mar 1879  F                                         W  15  1
          Supply Mistress Of Domestic Subjects Under London County Council Until Evacuation Of Children
Margaret M  Drake     03 Sep 1917  F  Secretary To Spg 15 Tufjon St W        S  15  2
Emily       Robinson  24 Apr 1857  F  Unpaid Domestic Duties                 W  15  3

1939 Ref RG101/0630B/002/29

Comments:
  1. The mystery is why her birth date is so different from that given at baptism, when they must have known when Muriel was born.
     Mystery solved: A transcription error by using the date on the line above.  The form had the right date!
  2. This does not invalidate this identification of Muriel as her mother is known from the 1911 census and the baptism and Muriel was a teacher of Domestic Science before marriage.
  3. Her son John Paul was absent and not found in the 1939 Register.  This might have been either because he had been called up or he was a student at Oxford, though the latter should still have got him into this Register.
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Her death index from FindMyPast with the correctr birth date:

First name(s)  Muriel Alice
Last name      Drake
Gender         Female
Birth day      12
Birth month    6
Birth year     1879
Death quarter  2
Death year     1978
District       Sutton
County         Surrey
Volume         15
Page           0517
Country        England
Record set     England & Wales Deaths 1837-2007
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She was married for less than a sixth of her long life.
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Her probate index:

1978
DRAKE, Muriel Alice of Woodcote Grove House Coulsdon Sy died 3 April 1978  Probate London 14 June £4632  780112461W

Her will has been ordered.
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In her will she left everything to her son John Paul Deake and his wife Rosemary Etheldreda and made them the executors of her will.

She mentioned her long-dead husband, for her burial and otherwise no other people were mentioned.
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Their marriage index:

First name(s)       Frederick W
Last name           Drake
Marriage quarter    1
Marriage year       1915
Marriage Finder     Frederick W Drake married one of these people
                    Muriel A Robinson
Spouse's last name  Robinson
District            St. George Hanover Square
County              London
Country             England
Volume              1A
age number          868
Record set          England & Wales Marriages 1837-2005
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She appeared for a Marriage Licence:

“DIOCESE OF LONDON

“APPEARED PERSONALLY Muriel Alice Robinson of the Parish of St Paul Knightsbridge in the County of Middlesex a Spinster of the age of twenty one years and upwards and prayed a Licence for the solemnization os Matrimony in the Parish Church of St Paul Knightsbridge aforesaid between her and Frederick William Drake of the Parish of Kirby Misperton in the County of York a Bachelor of the age of twenty one years and upwards and made Oath that she believeth that there is no impediment of Kindred or Alliance, or of any other lawful cause, nor any Suit commenced in any Ecclesiastical Court to bar or hinder the Proceeding of the said matrimony, according to the tenor of such Licence.  And she further made Oath, that she the said appearer hath had her usual Place of abode within the said Parish of St Paul Knightsbridge for the space of Fifteen days last past
  …  Muriel. a. Robinson
Sworn at 1, Dean’s Court, Doctors’ Commons
London, on the 23rd day
of October 1914
      Before me   H E Tayler
                  Ch. Clerk
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